There is an increasing interest in recycling waste plastic objects such as used plastic containers. Generally, the recycling of such materials requires that they be sorted as to the type of plastic used to make them. Many plastic containers now have a symbol imprinted upon them identifying the type of plastic used to make them so that consumers or recycling plant operators can manually sort the containers for recycling. Automated sorting methods and apparatus have been developed for waste plastic materials based on various identification technologies such as infrared spectroscopy and X-ray fluorescence techniques.
Automated sorting methods and apparatus have been developed for agricultural products based on near-infrared absorption spectroscopy. Plastic materials have been identified as to whether they are linear polymers, e.g., polyethylene, or cyclic polymers, e.g., polystyrene, by near-infrared reflectance spectroscopy.